The prior art, such as, for example, unexamined Japanese Patent Publication HEI 1-51876, describes an imaging device for recording and reproducing slow motion pictures which uses a charge coupled device (CCD). The charge couple device of the Japanese document uses horizontal transfer clock and vertical transfer clock signals which are both N times as fast as the clock signals used for normal operation. As a result, the imaging device provides a video signal which is compressed along the time-axis. The compressed video signal is recorded in a conventional video tape recorder. In a reproducing mode, the compressed video signal is expanded along the time-axis by N times. Therefore, a slow motion picture which is N times slower than the normal operation is achieved.
In the prior art system, to obtain the compressed video signal, the CCD needs to have vertical and horizontal transfer clock signals which are N times faster (in frequency) than the clock signals used for normal operation. As a CCD is essentially a capacitive load device, a higher frequency drive signal, especially the horizontal transfer clock signal, results in higher power consumption.
Further, when the frequency of the drive signal, especially the horizontal transfer clock signal, is higher than a certain level, the efficiency in the transfer operation of the CCD is substantially reduce. This means that image information is lost during a transfer operation of the CCD. As a result, such prior art systems do not provide a high slow motion ratio. The slow motion ratio is defined as the time ratio between the time needed to derive one picture from the CCD in the normal operation mode and the time needed to derive one picture from the CCD in the slow motion mode. For example, if the necessary time in the normal operation mode is 1/60 second and the necessary time in the slow motion mode is 1/120, the slow motion ratio equals two.